Thanks for the information on sawflies Geoff - and congratulations on the stunning sawfly example.
Sorry to hear about your back, I've had 3 different family experiences: my wife who had a 6 hour not entirely successful surgery many years ago that left her pain free but less mobile, myself (also some years ago) who was relieved when the GP prescribed a course of high dose ibuprofen that did the trick, and my sister (in the last month) who was probably the most severely affected but had short, uneventful, and successful surgery.
Best wishes for a successful outcome by whatever pathway.